Effect of Warm Temperatures on Externally Bonded FRP Strengthening: Fid-Bau Portal

Effect of Warm Temperatures on Externally Bonded FRP Strengthening

Stratford, T. J. / Bisby, L. A.

Abstract

Fiber-reinforced polymer (FRP) plate strengthening relies critically upon the adhesive that is used to bond it to the existing structure. A typical two-part ambient-cure epoxy adhesive for structural strengthening has a glass transition temperature of approximately 40°C–70°C, but the stiffness and strength of the adhesive typically decrease at temperatures somewhat below this characteristic temperature. This paper investigates the implications of the changes in adhesive properties at warm temperatures ( $< 100 ° C$ ) for FRP-strengthened beams, through short-term experimental and analytical work. Tests were conducted on FRP-strengthened steel beams subjected to sustained load and increasing temperature; the results, however, are also relevant to strengthened concrete beams. Digital image correlation was used to measure the slip between the strengthening plate and beam, and hence to observe the behavior of the adhesive joint. A bond analysis was also developed to predict the slip across the adhesive joint at an elevated temperature, based upon the glass transition characteristics of the adhesive measured using dynamic mechanical analysis. The analysis allows the response of the strengthened beams to warm temperatures to be examined in further detail. Both the experimental and analytical results show that substantial slip can occur between the plate and beam at temperatures over 40°C. As the temperature increases and the adhesive softens, a greater length of adhesive joint is required to transfer load from the plate to the beam, resulting in an increase in slip that eventually causes debonding of the plate from the beam.